JPH09266666A - Step-up circuit and control circuit thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of parts of a step-up circuit, and to improve the efficiency of a power supply. SOLUTION: This step-up circuit has a control circuit 400 for switching and a conversion circuit 500 for voltage. The control circuit is constituted by a push-pull manner of a constant-current on type transistor Tr1 and a differential pulse on type Tr2. The conversion circuit 500 is composed of a N-P-N type switching transistor Tr3, a coil L1, a diode D1 and an electrolytic capacitor C2. When the on period of the switching transistor Tr3 is represented by Tn and an off period by Tf, output voltage reaches Vcc(Tn+Tf)/Tf. Since the constant-current on type transistor Tr1 is placed at a section nearer to a power supply than the differential pulse on type transistor, the switching transistor Tr3 can be driven directly, and the P-N-P transistor is unnecessitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a booster circuit and its control circuit. The present invention particularly relates to a booster circuit that stores energy in an inductance element when an NPN type switching transistor is on, and superimposes this energy on an input voltage to take out the energy to an output side when it is off, and a control circuit therefor.

[0002]

2. Description of the Related Art From the history of switching power supplies for electronic devices, a step-down circuit has been widely used before a step-up circuit. For example, a DC / DC converter that steps down a voltage such as 12V once generated for an LCD panel and generates 5V for a general IC is an example.

FIG. 4 is a diagram showing a configuration example of such a conventional step-down circuit. This configuration is roughly classified into a control circuit 100 that controls switching operation and a conversion circuit 200 that actually performs voltage conversion. The control circuit 100 includes a transistor Tr21, a transistor Tr22, and a capacitor C.
10 inclusive. On the other hand, the conversion circuit 200 includes a PNP type switching transistor Tr24, a diode D10, a coil L10, and an electrolytic capacitor C20.

Transistor Tr21 of control circuit 100
Is momentarily turned on by a differential pulse appearing at the right end of the capacitor C10 (hereinafter, this transistor is also referred to as "differential pulse-on type transistor"). On the other hand, the transistor Tr22 constitutes a part of a constant current circuit (not shown), and when turned on, supplies a constant current (hereinafter, also referred to as “constant current on-type transistor”). Transistor Tr21
Turns on when the switching transistor Tr24 should be turned on, and conversely turns on the transistor Tr22 when it should be turned off. Therefore, the transistor Tr2
1 and Tr22 form a push-pull circuit. The on / off instruction of the switching transistor Tr24 is given by a switching instruction signal (not shown) (hereinafter simply referred to as “instruction signal”) input to the control circuit 100.

The conversion circuit 200 steps down the power supply voltage Vcc according to the ratio of the on / off period of the switching transistor Tr24, and the stepped down voltage Vout is the diode D1.
Appears at 0 negative electrode. Here, if the ON period of the switching transistor Tr24 is Ton and the OFF period is Toff, Vcc and Vout have the following relationship.

Vout = Vcc · Ton / (Toff + Ton) (Formula 1) A PNP transistor is used as the switching transistor because the voltage drop of Vout with respect to Vcc is within the saturation voltage of the transistor.
If the NPN type is used, the voltage drop will increase to V _BE ,
Power efficiency drops. In addition, the switching transistor T
constant current on-type transistor T for turning on r24
The switching transistor Tr2 uses r22.
This is to ensure a stable step-down operation by making the current flowing through 4 constant. On the other hand, the reason why the differential pulse-on transistor Tr21 is used is to shorten the time required until the switching transistor Tr24 is turned off. This is to reduce the time taken for the transistor to pass through the non-saturation region and increase the efficiency of the power supply. Further, since the differential pulse-on type transistor has a short on-state period, it is advantageous in that power consumption is kept to a minimum.
The above is an example of the step-down circuit.

However, in recent years, along with the miniaturization and portability of personal devices, the number of devices using a battery as a primary power source has increased. In such a device, for example, there is a case where an IC of 5V drive exists in the load circuit although the primary side power supply is only 3V. Therefore, the demand for the booster circuit is expanding.

FIG. 5 is a diagram showing a configuration example of a conventional booster circuit. This configuration follows the existing step-down circuit in FIG. 4, and the control circuit 100 is the same. Conversion circuit 300
However, the constituent members and the arrangement thereof are close to those of the conversion circuit 200 of FIG.

1. In the conversion circuit 300, the switching transistor is the NPN type transistor Tr23,
While this is on, energy is stored in coil L11. When this is turned off, the stored energy is superimposed on the power supply voltage Vcc, and a voltage higher than Vcc appears at the negative electrode of the diode D11. Ton and Toff used in Equation 1
Therefore, Vcc and Vout have the following relationship.

Vout = Vcc · (Ton + Toff) / Toff (Equation 2) 2. The transistor Tr24 in FIG. 4 is also present in FIG. 5, but this transistor is a switching transistor Tr24.
It plays the role of an inverter for operating 23.
A resistor R10 is provided to determine the base voltage of the transistor Tr23.

[0011]

As described above, the boosting operation can be performed by the configuration of FIG. On the other hand, there is still a strong demand for further extending the battery operating time of electronic devices. The present invention has been made in order to meet this demand, and an object thereof is to provide a new booster circuit and its control circuit from a viewpoint different from the conventional development of designing a booster circuit based on a step-down circuit. To do.

[0012]

[Means for Solving the Problems]

(1) For this purpose, the control circuit of the booster circuit of the present invention stores energy in the inductance element when the NPN type switching transistor is on, superimposes this energy on the input voltage when it is off, and outputs it. A circuit for controlling the booster circuit taken out to, wherein the NPN-type first transistor that turns on a constant current only when the instruction signal for instructing the switching transistor to turn on and off instructs a constant current, and the instruction signal are A second transistor of NPN type that is turned on transiently only when instructing to turn off, the emitter of the first transistor is connected to the collector of the second transistor, and these transistors are arranged in this order between the power supply and ground. However, the emitter of the first transistor is directly connected to the base of the switching transistor.

According to this configuration, the constant current ON type transistor (first transistor) and the differential pulse ON type transistor (second transistor) are opposite to those of the conventional general control circuit. Therefore, the PNP type transistor used as an inverter in the conversion circuit is unnecessary.

With this configuration, the first transistor is turned on when the instruction signal instructs the switching transistor to be turned on. Since the emitter of the first transistor is connected to the base of the switching transistor, when the first transistor turns on, the switching transistor also turns on. On the other hand, when the instruction signal indicates off, the first transistor is turned off and the second transistor is turned on transiently. When the second transistor is turned on, the electric charge of the base of the switching transistor is extracted, so that the switching transistor is turned off rapidly. As a result, the switching operation is realized.

(2) On the other hand, in the booster circuit of the present invention, the NPN type switching transistor whose collector is grounded and the switching transistor is turned on and turned on only when the instruction signal for instructing the on / off of the switching transistor is turned on. An NPN type first transistor that allows a current to flow, and a NPN type second transistor whose collector is connected to the emitter of the first transistor and the base of the switching transistor and which is turned on transiently only when the instruction signal indicates off. , An inductance element whose one end is connected to the collector of the switching transistor and whose other end is connected to the power supply,
Including a diode whose positive electrode is connected to the collector of a switching transistor, and a capacitor whose one end is connected to the negative electrode of the diode and whose other end is grounded, which boosts the power supply voltage and takes it out at the negative electrode of the diode Is.

In this structure, the switching transistor is turned on when the instruction signal gives an instruction to turn on, and turned off when the instruction signal gives an off instruction is realized by the same operation as (1). Energy is stored in the inductance element when the switching transistor is on. When the switching transistor is turned off, the path of the power supply → the inductance element → the positive electrode to the negative electrode of the diode → the output is disconnected from the switching transistor, so that the sum of the power supply voltage and the voltage due to the stored energy appears on the output side. As a result, boosting is realized.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described. The conventional booster circuit shown in FIG. 5 is designed based on the step-down circuit shown in FIG. In the step-down circuit shown in FIG. 4, due to the problem of voltage drop, P is used as a switching transistor.
Adopted NP transistor. This remains as it is in the booster circuit of FIG. However, in the present embodiment, attention is paid to the fact that the PNP transistor is no longer a problem of voltage drop in FIG. 5, and the PNP transistor is eliminated by adopting another circuit configuration. Hereinafter, the present embodiment will be described with reference to the drawings as appropriate.

FIG. 1 is a block diagram of a booster circuit according to this embodiment. This circuit is also roughly divided into a control circuit 400 and a conversion circuit 500. The control circuit 400 is composed of a constant current on-type transistor and a differential pulse on-type transistor as in FIG. 5, but their positional relationship is reversed. That is, the first transistor Tr1 which is a constant current on-type transistor on the side closer to the power source and the second transistor Tr1 which is a differential pulse on-type transistor on the side closer to ground.
2 is provided, and a capacitor C1 for creating a differential waveform is placed at the base of the transistor Tr2. As these transistors, those whose operating speed is high and whose saturation voltage is low enough to meet the design specifications are selected. The capacitance order of the capacitor C1 is, for example, 1000 pF.

On the other hand, the conversion circuit 500 has a configuration in which the PNP transistor and the resistor R10 are removed from the conversion circuit 300 of FIG. 5, and the switching transistor is directly driven by the control circuit 100. That is, the conversion circuit 500 includes an NPN switching transistor T whose collector is grounded.
r3, a coil L1 which is an inductance element whose one end is connected to the collector of this transistor and whose other end is connected to a power source, and whose positive electrode is the switching transistor Tr3.
Includes a diode D1 connected to the collector of the diode D1 and an electrolytic capacitor C2 having one end connected to the negative electrode of the diode D1 and the other end grounded, which boosts the power supply voltage Vcc, which is taken out from the negative electrode of the diode D1. The same consideration is given to the operating speed and saturation voltage of these transistors. The inductance of the coil L1 is determined in consideration of the magnitude of the current to be passed and the allowable voltage ripple, and is, for example, 100 μH. The power supply voltage Vcc is, for example, 3V, and Vout is about 3V to several tens of volts. If the current flowing through the load circuit is 1 A by design, the current capacity of the diode D1 is 2 A or the like. The electrolytic capacitor C2 may be, for example, about 100 μF. Of course, this capacitor is not limited to an electrolytic capacitor, and any capacitor having a capacity and a withstand voltage equivalent to that may be used.

In this configuration, the positions of the constant current on-type transistor and the differential pulse on-type transistor are reversed, so that the PNP type transistor of FIG. 5 is omitted. In addition, since the transistors included in this configuration are all NPN type, PNP is generally used in terms of component size and operating speed.
It has advantages over molds.

The operation of the above configuration will be described.

First, when a switching instruction signal (not shown) instructs the switching transistor Tr3 to turn on, the transistor Tr1 turns on. Along with this, the switching transistor Tr3 is turned on. At this time, a current flows through the coil L1 due to the potential generated at both ends of the coil L1, and energy proportional to the square of this current and the inductance of the coil L1 is accumulated.

On the other hand, when the instruction signal instructs turning off, the transistor Tr1 turns off. At this time, on the contrary, the transistor Tr2 is transiently turned on based on the differential pulse. As a result, the electric charge accumulated in the base of the switching transistor Tr3 is rapidly extracted, and the switching transistor Tr3 is turned off. In this way, the switching operation is realized. The relationship between Vout and Vcc is as shown in Equation 2.

FIG. 2 is a diagram showing a detailed configuration of the booster circuit shown in FIG. 1, in which a configuration example of a constant current circuit and a differential pulse generation circuit is illustrated. The switching instruction signal is indicated by "CNT signal" in the figure, and when this signal is high, the switching transistor is turned on, and when it is low, it is turned off. The constant current circuit is
Transistors Tr5 to 8 forming a current mirror circuit
And a transistor Tr1 and a resistor R1,
When the NT signal is high, a constant current determined by the current flowing through the resistor R1 flows through the transistor Tr1.

On the other hand, in the differential pulse generation circuit, a transistor Tr4 controlled by a CNT signal, a resistor R2 pulling up the collector of this transistor, a capacitor C1 having one end connected to the collector, and a negative electrode connected to the other end, It is composed of a diode D2 whose positive electrode is grounded. The base of the transistor Tr2 is connected to the negative electrode of the diode D2. Considering the rough operation, if the CNT signal is low, the transistor Tr4 turns off, and V1 in the figure
And V2 become high, the transistor Tr2 is turned on, and the switching transistor Tr3 is accelerated to be turned off.

FIG. 3 is a voltage or current waveform diagram of the main part of the booster circuit accompanying a change in the CNT signal. V1 in FIG. 2 is shown in FIG.
Is a collector voltage of the transistor Tr4, V2 is a base voltage of the transistor Tr2, V3 is a base voltage of the switching transistor Tr3, and i2 and i3 respectively represent currents flowing into the bases of the transistors Tr2 and Tr3. In the figure, the high period and the low period of the CNT signal are set to be equal, and in this case, Vout is 2 from Equation 2.
It becomes Vcc. First, the description will focus on the voltages V1 to V3.

At time t1 in the figure, when the CNT signal changes to high or low, the transistor Tr5 turns off,
The transistor Tr1 is also turned off. At t1, the transistor Tr4 is turned off, and V1 is the resistor R2 and the capacitor C.
It gradually increases according to the time constant determined by 1. V2 is V1
Since it reacts differentially with respect to the change of, it rapidly rises at t1. In this circuit configuration, V2 rises above 0V because there is no reason to stop at 0V, but transistor Tr
With V _BE of 2, it stops at 0.7V. The rise of V2 turns on the transistor Tr2 and the fall of V3.
The switching transistor Tr3 is turned off.

Subsequently, when the CNT signal becomes high at time t2, the transistor Tr4 is turned on and V1 suddenly drops to low. In response to this change, V2 also drops.
V2 drops below 0V because there is no reason to stop at ground voltage 0V, but it stops at -0.7V due to the presence of diode D2. The drop in V2 turns off the transistor Tr2, and V3 goes high. This turns on the switching transistor Tr3. After that, the same operation is repeated from t3 onward.

Consider the currents i2 and i3. First, at t1, V2 rises, so that i2 rapidly increases in the transistor Tr.
Pour into the base of 2. Therefore, the transistor Tr2 is momentarily turned on, and the electric charge is rapidly extracted from the base of the switching transistor Tr3. This is indicated by the fact that i3 in the figure instantaneously takes a large negative value. Thus, the switching transistor Tr3 is turned off faster,
The time to stay in the unsaturated region is shortened.

Then, when t2 is reached, the transistor Tr1 is turned on. However, since i2 flows as a differential pulse in the direction opposite to that at the time of t1, the transistor Tr2 is turned off at high speed, and the current penetrating from the power supply to the ground is minimized while both transistors Tr1 and Tr2 are on.

While the CNT signal is high, the transistor Tr1 is turned on and a constant current flows, while the transistor T1 is turned on.
Since r2 is off, i3 becomes a constant current. Therefore, the current supplied to the conversion circuit 500 side becomes known,
This is convenient for stabilizing the conversion operation and designing the circuit.

The above is the configuration and operation of the present embodiment. It should be noted that the present embodiment has a considerable degree of freedom in the configuration of the constant current circuit and the differential pulse generation circuit. In addition, the booster circuit of this embodiment can be integrated in whole or in part as an IC in whole or in part. As an example of an IC, the control circuit 40 shown in FIG.
There is a method in which the part of 0 except the resistor and the capacitor is integrated and the resistor and the capacitor are externally attached. This method is convenient because the resistor and the capacitor can be selected according to the design.

[0033]

In the control circuit of the booster circuit according to the present invention, the constant current on-type transistor and the differential pulse on-type transistor are arranged in the opposite manner to the conventional one, so that it is not necessary to use the PNP transistor on the conversion circuit side. Therefore, the power consumed by this transistor can be saved and the power supply efficiency is improved. In addition, P, which generally has a large component size,
Since the NP transistor can be deleted, it is normally PN
There is also an advantage in semiconductor manufacturing technology, which is not good at manufacturing P-transistors.

On the other hand, the booster circuit of the present invention uses the control circuit described above, and can provide a circuit advantageous in terms of power supply efficiency, the number of parts, and integration. Therefore, various electronic devices, particularly DC / DC for portable video cameras, personal computers, audio devices, display devices, etc.
It can be used for various boosting circuits such as converters and AC / DC converters.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a booster circuit according to an embodiment.

FIG. 2 is a diagram showing a detailed configuration of the booster circuit of FIG.

FIG. 3 is a voltage or current waveform diagram of a main part of a booster circuit according to a change in a CNT signal.

FIG. 4 is a diagram showing a configuration example of a conventional step-down circuit.

FIG. 5 is a diagram showing a configuration example of a conventional booster circuit.

[Explanation of symbols]

Tr1, 2, 4-8 transistors, Tr3 switching transistors, C1 capacitors, C2 electrolytic capacitors, L1 coils, D1, 2 diodes, R1,
2 resistors, 400 control circuit, 500 conversion circuit.

Claims (2)

[Claims] 1. When the NPN type switching transistor is on, energy is stored in the inductance element,
A circuit that controls the booster circuit that superimposes this energy on the input voltage when it is off and takes it out to the output side.It is turned on only when the instruction signal that instructs the switching transistor to turn on or off turns on. An NPN type first transistor that allows a current to flow, and an NPN type second transistor that is turned on transiently only when the instruction signal indicates an off state, the emitter of the first transistor being a collector of the second transistor. A control circuit that is connected and these transistors are arranged in this order between the power supply and ground, and the emitter of the first transistor is directly connected to the base of the switching transistor. 2. An NPN type switching transistor having a collector grounded, and an NPN type first transistor which turns on a constant current only when an instruction signal for instructing on / off of the switching transistor indicates on. A collector is connected to the emitter of the first transistor and a base of the switching transistor, and an NPN type second transistor that is turned on transiently only when the instruction signal indicates off, and one end is connected to the collector of the switching transistor A power supply voltage including an inductance element whose other end is connected to a power supply, a diode whose positive electrode is connected to the collector of the switching transistor, and a capacitor whose one end is connected to the negative electrode of the diode and whose other end is grounded. Is boosted, and this is taken out at the negative electrode of the diode. Booster circuit characterized by: